Zeolites, and in particular mordenites, are used as catalysts in chemical processes, such as in carbonylation reactions of ethers and alcohols. For example EP 1985606 describes the production of methyl acetate by carbonylating dimethyl ether with carbon monoxide in the presence of zeolite catalysts, such as mordenites, at temperatures of greater than 250° C. to 350° C. and at pressures of at least 10 barg.
Mordenites are crystalline natural or synthetic zeolites of the aluminosilicate type. The mordenite structure is defined in the Atlas of Zeolite Framework Types (C. Baerlocher, W. M. Meier, D. H. Olson, 5th Ed. Elsevier, Amsterdam, 2001). Generally mordenites have a composition expressed in moles of oxide of1.0±0.2Na2O,Al2O3,10±0.5SiO2 Instead of sodium other alkali or alkaline earth metals may also be present.
In general, the sodium form of mordenite is not particularly effective for the carbonylation of ethers and it has been found that replacing some or all of the sodium cations by hydrogen ions yields the more effective hydrogen form mordenite. Conversion of the sodium form to the hydrogen form can be accomplished by a number of means. One method is the direct replacement of sodium ions with hydrogen ions using an acidified aqueous solution where the process of ion-exchange is employed. Another method involves replacement of the sodium ions by ion-exchange with ammonium ions followed by decomposition of the ammonium form using a calcination method.
Catalysts for the carbonylation of ethers and alcohols can be prepared by combining commercially available hydrogen form mordenites with suitable binder materials, as described for example WO 2010/058149.
WO 2010/058149 describes a process for the preparation of methyl acetate and/or acetic acid by carbonylating dimethyl ether and/or methanol with carbon monoxide in the presence of a catalyst which catalyst is a H-mordenite bound with a mesoporous binder selected from silicas, aluminas, silica-aluminas, magnesium silicates and magnesium aluminium silicates.
An important aspect of any catalytic process is the performance of a catalyst when exposed to the desired process conditions. The improvement of catalytic performance in carbonylation reactions is a continuous objective of process and catalyst development research.
Mixtures of carbon monoxide and hydrogen (generally referred to as synthesis gas). are produced commercially and are readily available. Thus, it is desirable to conduct carbonylation processes using such synthesis gas mixtures. Typically, however, the synthesis gas mixtures are hydrogen-rich, that is hydrogen is present in such mixtures in at least an equimolar ratio and generally in an excess molar ratio to carbon monoxide. However, a hydrogen-rich feed means less space for carbon monoxide in the carbonylation reactor resulting in a reduced partial pressure of carbon monoxide and consequently a reduced rate of reaction. Thus, one problem which exists in carbonylation processes is that conducting the process under hydrogen-rich conditions increases the performance requirements of the catalyst.